fiesta heater problem

The heater in my wifes 2000 fiesta is blowing hot all the time,originaly it was blowing cold so changed thermostat,but did not cure problem so replaced heater control valve and now just blows hot all the time no matter what position the heater dial is in,had the control in car checked by sparky at work and he said it was ok,but when i replaced the hcv i got it off flea bay, not a ford part.all the problems with the heater appear to be with them blowing cold not hot, anyone have any ideas ?